When a conventional fluorescent lamp breaks, fragments of the glass tube, mercury, and phosphor powders from the lamp can scatter to contaminate a wide area. Such contamination is particularly damaging in areas where food is stored uncovered and to food preparation surfaces.
To reduce the possibility of scattered contamination by a broken fluorescent lamp, shatter-resistant lamp assemblies have been developed to contain the contents of a lamp when it breaks. Known lamp assemblies are shown in U.S. Pat. No. 4,048,537 (Blaisdell et al.), U.S. Pat. No. 4,924,368 (Northrop, et al.), U.S. Pat. No. 5,536,998 (Sica), and U.S. Pat. No. 5,173,637 (Sica). The Sica patents are owned by the assignee of the present invention.
The prior art protective assemblies for fluorescent lamps include special molded plastic end fittings that fit onto the terminal caps of the lamp and hold in place a protective sleeve encasing the lamp.
In some of the prior art devices, end fittings are intentionally designed to be removed from one lamp and reused on other lamps. This is very unsatisfactory and results in leakage and contamination by the lamp contents which escape when the lamp is broken.
The assemblies shown in the two Sica patents are a great improvement, the end fittings are sealed to the protective sleeve and to the lamp itself so that there is little leakage or contamination; the lamp contents are sealed in the sleeve.
A significant disadvantage of the three-component protective assemblies, i.e., sleeve and two end fittings, is the difficulty and expense of making them. The two end fittings can be relatively expensive to make, and the dimensions of the end fittings and sleeves should be matched to within relatively close tolerances to ensure a tight fit. Also, there are four seals to be formed, and the greater the number of seals, the greater the chances for leakage.
A long-standing problem with the three-component construction is that it gives the lamp bulbs an unnatural appearance and this, in turn, tends to impede their sales.
One prior proposal to solve this problem is to coat the entire bulb with a protective coating. However, this is unsatisfactory, in that the coating can reduce the useful light output from the bulb, and can become discolored with age, thus adding to the unsightliness.
In typical prior methods, a plastic sleeve is slipped over a straight fluorescent bulb and is sealed at its ends to the ends of the fluorescent bulb.
Special problems are caused by the curved shape of bulbs such as U-shaped and circular fluorescent bulbs. Whenever there is any significant curvature to the bulb, the prior methods are impractical.